The present invention relates generally to internal combustion engine ignition systems and, more particularly, to a method and apparatus for identifying the cylinder in compression of a cylinder pair of an internal combustion engine having an even number of cylinders and a coil per plug (CPP) ignition system wherein each cylinder has an associated coil having a primary winding and a secondary winding which is connected to a spark producing device or spark plug operable to fire the cylinder.
Ever stricter emission control standards and fuel economy requirements demand precise control of internal combustion engines, particularly control of ignition and fuel injection systems. Engine control can be coupled to cylinder pairs in engines having an even number of cylinders with cylinder pairs being identified by a crankshaft position sensor and crankshaft mounted timing wheel. For more precise control, engine control systems must recognize the compression stroke of one of the cylinders of the engine, typically the number one cylinder. In the past, identification of the cylinders has been performed by a cylinder identification (CID) sensor which responds to indicia on a camshaft of the engine.
While a CID sensor could be used to provide both cylinder identification and engine position, unfortunately CID sensor determinations are not sufficiently accurate due to mechanical play in the gear trains or belts which drive the camshaft. To provide sufficient accuracy, the CID sensor is used in combination with a crankshaft position sensor and crankshaft mounted timing wheel. Due to the inaccuracies of the CID sensor leading to its inability to function independently of a crankshaft sensor, it would be desirable to be able to perform cylinder identification without the CID sensor such that the CID sensor and related expense could be eliminated.
To that end, U.S. Pat. No. 4,889,094 describes a method of recognizing the power stroke of an internal combustion engine by comparing a first signal that is synchronized with the crankshaft angle and a second signal that is modulated by the combustion events of the engine. By combining the first and second signals, a third signal identifying the first cylinder in an internal combustion engine having an odd number of cylinders is generated. Unfortunately, the described method is not applicable to an engine having an even number of cylinders.
There is thus a need for the identification of cylinders in internal combustion engines having an even number of cylinders which does not rely on a CID sensor.